1. Field of the Invention
The present invention relates to an optical ferrule, and, more particularly, to an optical ferrule which can couple optical fibers in a detachable manner without causing an optical loss.
2. Prior Art
To connect optical fibers at the time of constructing an optical communication system, single-core optical ferrules which connect optical fibers using an adapter as shown in FIG. 1 or multi-core MT (Mechanically Transferable) optical ferrules as shown in FIG. 2 are used. Those ferrules are produced as resin moldings.
In the case of the MT optical ferrule shown in FIG. 2, for example, a ferrule body 1 is produced as an integrated molding having a plurality of optical-fiber insertion holes and guide pin holes 2 having a diameter of about 700 xcexcm. In connecting optical fibers, the optical fibers are inserted into the optical-fiber insertion holes and securely adhered in the holes. Then, a connection end face 1a of each ferrule body 1 is mirror-polished using a lubricant containing, for example, diamond abrasive grains dispersed and a separate guide pin 3 is inserted into each guide pin hole 2. Then, the connection end faces of the ferrule bodies are connected to couple the optical fibers.
As the position of an optical fiber at the connection end face is positioned by the guide pins 3 in the case of the MT optical ferrule, the guide pin holes 2 should be formed with high precision at the time of molding the ferrule body 1. In the case where the position precision and size precision of the guide pin holes become lower, a deviation occurs between the optical axes of the optical fibers when the ferrule bodies are connected. This leads to an optical loss.
In the case of the single-core optical ferrule shown in FIG. 1, the connection precision of optical fibers is determined by the roundness, cylindricity and outside diameter of the periphery, the circularity of the optical-fiber insertion hole, the inclination of the optical-fiber insertion hole and so forth. This case also requires precise molding.
Conventional optical ferrules of those types have been manufactured by transfer molding of a thermosetting resin, such s epoxy resin, which has a small rate of shrinkage at the time of molding and a high size stability with time.
However, the transfer molding requires a time for a resin to be thermoset after it is fed into a mold, making the molding cycle longer. The transfer molding is therefore disadvantageous for mass production.
As a solution to this problem, an optical ferrule has appeared which is produced by using a polyphenylene sulfide resin which has an excellent size stability, fluidity and environment resistance and the injection molding that involves a short molding cycle.
In this case, to reduce the coefficient of thermal expansion of the optical ferrule, a large amount of silica is normally filled in the polyphenylene sulfide resin, yielding a resin composition which is in turn molded.
When the connection end face of the optical ferrule produced from such a material (resin composition) is polished, however, the filled silica is likely to come off at the time of polishing. This makes it difficult to provide a smooth end face.
One way to prevent silica from coming off is to subject silica to a surface treatment with a silane coupling agent before it is filled in the resin and use a mixture of spherical silica and irregular-shaped silica as the silica, as proposed in, for example, Japanese Unexamined Patent Publication No. Hei 6-299072.
The prior art still has the following problems.
First, the smoothness of the connection end face after polishing may not be sufficient so that the physical contact of the polished end faces of optical ferrules alone makes it difficult to realize proper optical coupling of optical fibers.
In connecting optical ferrules, therefore, conventionally a refractive-index matching agent, such as silicone grease, is coated on the polished end face to thereby prevent the refractive index from changing or the optical loss from occurring due to the contact of the optical path formed by the optical fibers with the air.
It is however necessary to carefully perform the work of coating the refractive-index matching agent in such a way that, for example, dust or the like does not enter the coated portion. Depending on the coating work, bubbles may be formed in the coated portion, resulting in a considerably large optical loss. In view of the above, there is a demand for development of optical ferrules which do not use a refractive-index matching agent or do not produce a clearance between optical fibers even when they are rendered in physical contact with each other, and do not cause an optical loss.
In consideration of the physical contact of the optical ferrule, an end portion of an optical fiber should protrude from the polished end face by about 3 to 5 xcexcm.
In the case of the above-described optical ferrule, however, a large amount of silica which has about the same hardness as the optical fiber is filled in the resin, the polished end face itself is hard so that at the time of polishing, the optical fiber is polished out and so is the polished end face. This may make the extension length of the polished optical fiber considerably shorter than the aforementioned value. In such a case, a clearance is formed in the connecting portion of the optical fibers, which leads to a significantly large optical loss.
It is known that at the time of polishing the end face of the optical ferrule, so-called edge chipping or chipping of the edge of an optical fiber appearing on the polished end face occurs. Because the polished end face is very hard, the polishing time becomes longer and the amount of abrasive grains increases. This results in an increased manufacturing cost.
Accordingly, it is an object of the present invention to provide an optical ferrule which overcomes the aforementioned problems of the conventional optical ferrules, has a very smooth polished end face and a proper extension length of an optical fiber after the end face is polished, does not suffer edge chipping of the optical fiber, can ensure connection without using a refractive-index matching agent and has a low optical loss between optical fibers even after connection.
To achieve the object, according to the present invention, there is provided an optical ferrule which is a molded product of a resin composition comprising 100 parts by mass of a polyphenylene sulfide resin, 100 to 300 parts by mass of silica having a maximum grain size of 100 xcexcm or smaller and 50 to 300 parts by mass of barium titanate.
It is preferable that in the optical ferrule, the silica should be spherical silica, the polyphenylene sulfide resin should be formed of linear polyphenylene sulfide, and the resin composition should essentially consist of 100 parts by mass of a linear polyphenylene sulfide resin, 100 to 200 parts by mass of spherical silica having a maximum grain size of 50 xcexcm or smaller and 150 to 250 parts by mass of barium titanate.